1. Field of the Invention
The invention relates to electrical laminates fabricated from copper sheets and reinforced thermosetting resins.
2. Description of the Prior Art
Electrical circuit boards are prepared by combining copper sheets or copper alloy sheets with sheets of lightweight electrical insulating materials such as glass fiber reinforced unsaturated polyester resin sheets. The electrical circuit board may have a sheet of copper foil on one side only or on both sides of the laminate.
A test for determining the peel strength of copper foil from electrical circuit boards has been established by National Electrical Manufacturers' Association, Test LI 1-10.14. Normally the copper foil is secured to the reinforced plastic sheet by means of a suitable adhesive. Attempts to cure an unsaturated polyester resin directly on a copper foil heretofore have not produced a resulting laminate with sufficient peel strength.
Benzotriazole has been employed in unsaturated polyester resin compositions which have been used to encapsulate electrical components.